The extraction of roasted and ground coffee for soluble coffee processing is most often carried out in a fixed bed countercurrent extraction battery having between six and eight columns. Hot extraction water, typically at a temperature in excess of 160.degree. C., is fed to the column containing the most spent coffee (that is, the coffee that has had the most solids extracted) so as to thermally hydrolyze the coffee. The extraction liquid progresses through columns containing increasingly less extracted coffee, becoming richer in coffee solids. The final column in the extraction train, from which coffee extract is withdrawn, contains the freshest (least extracted) coffee, which coffee is then atmospherically extracted. Periodically, after all the solids that are practically soluble and extractable have been removed from the spent coffee, the column containing said coffee is isolated from the battery and a new column containing fresh coffee is brought on stream. The flow of the extracting liquid is adjusted so that the hot extraction water is fed to the new most spent column and the corresponding adjustments made throughout the battery. Thus, the countercurrent extraction battery is not continuous and such a system requires considerable valving and piping (a complex manifold) to permit the desired flow adjustments. Typical countercurrent extraction batteries are described in U.S. Pat. No. 2,515,730 to Ornfelt and U.S. Pat. No. 2,915,399 to Guggenheim et al. as well as in "Coffee Processing Technology" by Sivetz and Foote, AVI Publishing, Westport, Conn., 1963, Vol. 1, pp 281-294.
It is an object of the present invention to extract soluble solids from roasted and ground coffee in a manner effective to preserve the flavor quality of said soluble solids.
It is another object of the present invention to provide a more nearly continuous method of extracting roasted and ground coffee, which method does not require the complex manifold associated with a conventional countercurrent extraction battery.
A further object of the present invention is to provide a method of extracting roasted and ground coffee which is more efficient than said countercurrent extraction battery, owing to the greater number of equivalent extraction stages practically obtainable with the method of the present invention.